The endozepine triakontatetraneuropeptide diazepam-binding inhibitor [17-50] stimulates neurosteroid biosynthesis in the frog hypothalamus.
Neurons and glial cells are capable of synthesizing various bioactive steroids, but the neuronal mechanisms controlling neurosteroid-secreting cells are poorly understood. In the present study, we have investigated the possible effect of an endogenous ligand of benzodiazepine receptors, the triakontatetraneuropeptide [17-50] (TTN), on steroid biosynthesis in the frog hypothalamus. Immunohistochemical studies revealed that most hypothalamic neurons expressing 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4-isomerase also contained peripheral-type benzodiazepine receptor-like immunoreactivity. Confocal laser scanning microscopic analysis revealed that the peripheral-type benzodiazepine receptor-immunoreactive material was located both in the cytoplasm and at the periphery of the cell bodies. By using the pulse-chase technique, TTN was found to stimulate the conversion of [3H]pregnenolone into various steroids, including 17-hydroxypregnenolone, 5 alpha-dihydrotestosterone and 17-hydroxyprogesterone, in a dose-dependent manner. The peripheral-type benzodiazepine receptor agonist Ro5-4864 mimicked the stimulatory effect of TTN on the formation of neurosteroids. The peripheral-type benzodiazepine receptor antagonist PK11195 significantly reduced the effect of TTN on neurosteroid synthesis, while the central-type benzodiazepine receptor antagonist flumazenil did not affect the formation of neurosteroids evoked by TTN. These data indicate that TTN stimulates the biosynthesis of 3-keto-17 alpha-hydroxysteroids in frog hypothalamic neurons through activation of peripheral-type benzodiazepine receptors likely located at the plasma membrane level.
Do-Rego
J L
JL
European Institute for Peptide Research (IFRMP no 23), Laboratory of Cellular and Molecular Neuroendocrinology, INSERM U 413, UA CNRS, University of Rouen, Mont-Saint-Aignan, France.
Mensah-Nyagan
A G
AG
Feuilloley
M
M
Ferrara
P
P
Pelletier
G
G
Vaudry
H
H
D015096:3-Hydroxysteroid Dehydrogenases / Q000378:metabolism; D000818:Animals; D001570:Benzodiazepinones / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D003292:Convulsants / Q000494:pharmacology; D019085:Fluorescent Antibody Technique, Direct; D058787:GABA-A Receptor Antagonists; D007031:Hypothalamus / Q000187:drug effects / Q000378:metabolism*; D007150:Immunohistochemistry; D008297:Male; D009479:Neuropeptides / Q000494:pharmacology*; D010446:Peptide Fragments / Q000494:pharmacology*; D010525:Peripheral Nerves / Q000201:enzymology / Q000378:metabolism; D011895:Rana ridibunda; D011963:Receptors, GABA-A / Q000378:metabolism; D013256:Steroids / Q000096:biosynthesis*; D013268:Stimulation, Chemical
D001570:Benzodiazepinones; D003292:Convulsants; D058787:GABA-A Receptor Antagonists; D009479:Neuropeptides; D010446:Peptide Fragments; D011963:Receptors, GABA-A; D013256:Steroids; C060941:triakontatetraneuropeptide; C028513:4'-chlorodiazepam; D015096:3-Hydroxysteroid Dehydrogenases